1. Field of the Invention
The present invention relates to touch panels for display devices. More particularly, the present invention relates to combination resistive-type and electromagnetic type touch panels for display devices.
2. Discussion of the Related Art
Touch panels have been developed as a means of efficiently interfacing with electronic devices via a display surface. For example, users may input desired information using a touch panel integrated with a display device while watching images displayed by the display device. Allowing users to input desired information to an electronic device via a display surface, touch panels substantially reduce or eliminate the need for other types of input devices (e.g., keyboards, mice, remote controllers, and the like). Currently, touch panels have been widely integrated with display surfaces of flat panel display devices such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescence (EL) devices, and cathode ray tubes (CRTs).
Depending on the type of contact object used (e.g., a user's finger, a stylus, etc.), and depending on the manner in which the location of a contact point (i.e., the location where the contact object is operably proximate the touch panel) is determined, touch panels are generally classifiable as analog resistive-type, capacitive-type, electromagnetic (EM)-type, saw-type, and infrared-type touch panels.
Generally, analog resistive-type touch panels include an upper transparent substrate supporting an upper electrode and a lower transparent substrate supporting a lower electrode. The upper and lower transparent substrates are attached to each other but spaced apart from each other by a predetermined distance. When a surface of the upper transparent substrate is contacted by a contact object, an upper electrode formed on the upper transparent substrate electrically contacts a lower electrode formed on the lower transparent substrate. When the upper and lower electrodes electrically contact each other, a voltage, made variable by a resistance value or a capacitance value specific to the location of where the contact object contacted the touch panel (i.e., the contact point), is then detected and outputted along with a location defined by coordinates of the contact point.
Generally, capacitive-type touch panels include a transparent electrode formed on a display device such as an LCD panel, wherein a voltage is applied to each corner or side of the transparent electrode and a uniform electric field is thereby generated within the transparent electrode. Coordinates of the contact point are determined in accordance with a voltage drop generated when the user touches the touch panel via the contact object.
FIG. 1 illustrates a cross-sectional view of a related art resistive-type touch panel. FIGS. 2A to 2C illustrate a method by which a contact point location on a related art resistive-type touch panel is detected.
Referring to FIG. 1, related art resistive-type touch panels generally include an upper substrate 20, a lower substrate 30, and a plurality of dot spacers 50. The upper and lower substrates 20 and 30 are typically formed of an elastic material such as PET, thin glass films, etc. Upper and lower substrates 20 and 30 formed of thin glass films have isotropic optical properties. Recently, however, plastic films having isotropic optical properties have been used as upper and lower substrates 20 and 30. A polarizing plate (not shown) is usually formed on the surface of the glass substrate to decrease surface reflectivity of the resistive-type touch panel. A first transparent electrode 21 is formed on a lower surface of the upper substrate 20 while a second transparent electrode 22 is formed on an upper surface of the lower substrate 30. The upper and lower substrates 20 and 30 are boded to each other via an adhesive material 40 having a thickness of 75 μm to 200 μm. The plurality of dot spacers 50, spaced apart from each other by a distance of between 100 μm and 300 μm, are formed between the upper and lower substrates 20 and 30 to electrically insulate the upper substrate 20 from the lower substrate 30 during an initial state. However, when a contact object “B” (e.g., a stylus pen) contacts and presses upon a portion the upper substrate 20 “A”, a portion of the upper substrate 20 contacts the lower substrate 30, as shown in FIG. 2A. Further referring to FIG. 2A, a signal line 60 is provided between the upper and lower substrates 20 and 30 within the adhesive material 40.
Referring to FIG. 2B, first metal electrodes 80 are formed in left and right peripheral regions of the upper substrate 20 and second metal electrodes 70 are formed in upper and lower peripheral regions of the lower substrate 30.
Referring to FIG. 2C, the coordinates of any contact point generated on the aforementioned related art resistive-type touch panel are determined using two pairs of resistors (Rx1, Rx2) and (Ry1, Ry2) connected in series, a power source terminal, and a switching part S. The power source terminal applies a voltage (Vx, Vy) to predetermined ones of the resistor pairs via the switching part S.
Referring to FIGS. 2A to 2C, when a contact point “A” is generated with a contact object “B” (e.g., stylus pen), the upper substrate 20 contacts the lower substrate 30 at contact point “A”. Next, an X-axis voltage Vx is applied between the second metal electrodes 70 of the lower substrate 30 and a potential gradient is thereby generated on a an electrically resistive surface between the second metal electrodes 70. Accordingly, a resultant voltage is received by the first metal electrode 80 of the upper substrate 20 and transmitted to a controller where an X-axis coordinate of the contact point “A” is calculated. Next, a Y-axis voltage Vy is applied between the first metal electrodes 80 of the upper substrate 20 and a potential gradient is thereby generated on an electrically resistive surface between the first metal electrodes 80. Accordingly a resultant voltage is received by the second metal electrodes 70 of the lower substrate 30 and transmitted to the controller where a Y-axis coordinate of the contact point “A” is calculated. As a result, the location of the contact point “A” on a display surface is determined. With the location of the contact point “A” determined, the contact point “A” may be displayed at a corresponding position by the display surface. The process described above is repetitively performed at a high speed, thereby allowing the location of the contact point “A” to be continuously determined and displayed by the display surface. As a result, a user can write letters, draw lines, etc. on the display surface via the related art resistive-type touch panel.
FIG. 3 illustrates a cross-sectional view of a resistive-type touch panel integrated with a liquid crystal display (LCD) device.
Referring to FIG. 3, the aforementioned related art resistive-type touch panel is integrated with an LCD device having an LCD panel, wherein the LCD panel and the resistive-type touch panel are secured together by a case top. Accordingly, a related art resistive-type touch panel integrated with an LCD device includes an LCD panel 41, an upper polarizing plate 42, a lower polarizing plate 43, a backlight 44, a resistive-type touch panel 45, and a metal case top 46.
The LCD panel 41 is capable of displaying images in accordance with externally input driving and video signals and includes upper and lower substrates bonded to each other and spaced apart from each other by a predetermined distance, wherein liquid crystal material is injected between the upper and lower substrates. The upper polarizing plate 42 is arranged over the LCD panel 41 and the lower polarizing plate 43 is arranged beneath the LCD panel 41 to selectively polarize light irradiated by the backlight 44 into the LCD panel 41 as well as emitted light transmitted by the LCD panel 41. The resistive-type touch panel 45 is formed above the LCD panel 41 and outputs a variable voltage in accordance with a location of the contact point on the touch panel. The case top 46 is provided as a metal material that secures the backlight 44, the LCD panel 41, and the resistive-type touch panel 45 together as a single body.
As mentioned above with respect to FIGS. 1-2C, the resistive-type touch panel 45 includes transparent electrodes (not shown) formed on opposing surfaces of bonded upper and lower substrates 47 and 48. A plurality of dot spacers 49 formed within a viewing area between the upper and lower substrates 47 and 48 to uniformly maintain the distance between the upper and lower substrates 47 and 48. The upper and lower substrates 47 and 48 are bonded to each other via an adhesive material (not shown) provided in a dead space region.
Touch panels are integrated with display devices based on their suitability for a given application. For example, the related art resistive-type touch panel is beneficially integrated with display devices used where low price, high yield, comfortable writing sensation, etc., are important considerations. However, the related art resistive-type touch panels are not suitably integrated with all types of display devices. For example, an electromagnetic (EM)-type touch panels are beneficially integrated with industrial display devices where requiring electro-optical, insulating and endurance characteristics.
FIG. 4 illustrates a cross-sectional view of a related art electromagnetic (EM)-type touch panel.
Referring to FIG. 4, a related art EM-type touch panel is integrated with a display device such as an LCD device, wherein the LCD device includes an LCD panel 51, an upper polarizing plate 52, a lower polarizing plate 53, a backlight 54, a passivation layer 55, an EM-type touch panel 56, and a case top 57.
The LCD panel 51 is capable of displaying images in accordance with externally input driving and video signals and includes upper and lower substrates bonded to each other and spaced apart from each other by a predetermined distance, wherein liquid crystal material is injected between the upper and lower substrates. The upper polarizing plate 52 is arranged over the LCD panel 51 and the lower polarizing plate 53 is arranged beneath the LCD panel 53 to selectively polarize light irradiated by the backlight 54 into the LCD panel 51 as well as emitted light transmitted by the LCD panel 51. Arranged above and spaced apart from the upper polarizing plate 52, the passivation layer 55 serves as a dielectric layer as well as protects the LCD panel 51 from a proximately arranged stylus pen 63, as will be discussed in greater detail below. The EM-type touch panel 56 is arranged below the LCD panel 51 and outputs a variable voltage in accordance with a location of the contact point on the touch panel. The case top 45 is provided as a metal material that secures the backlight 54, the LCD panel 51, and the EM-type touch panel 56 together as a single body.
The EM-type touch panel 56 includes a sensor board 62 having a sensor PCB 58, a shield plate 59, and a connector 61 to generate electromagnetic fields; and a control board 64 having a microprocessor 66 for transmitting signals to the sensor board 62 and for detecting coordinates of contact point generated by a stylus pen 63 by detecting input signals generated by the stylus pen 63, wherein the stylus pen 63 includes a resonance circuit 65 having a coil and a capacitor. The electromagnetic field generated from the sensor board 62 is stored in the resonance circuit 65 of the stylus pen 63 for a predetermined amount of time.
During operation of the related art EM-type touch panel shown in FIG. 4, a control signal is generated by the control board 64 which, in turn, enables the sensor board 62 to generate an electromagnetic field. Subsequently, a current is induced within a stylus pen 63 arranged within the generated electromagnetic field, wherein the induced current has a resonant frequency and is stored for a predetermined amount of time in accordance with an LC value of the resonance circuit 65. The sensor board 62 then detects the induced current stored within the resonance circuit 65 and transmits a corresponding signal to the control board 64 whereby the control board 64 determines the location of the contact point generated by the stylus pen 63.
The resonance circuit 65 is provided as an LRC circuit, wherein the amplitude of the induced current varies with the frequency of an applied power source. The amplitude of the induced current is maximized at a predetermined resonance frequency (f) of the applied power source. More specifically, the resonance frequency (f) is determined by the following equation:f=(2π√{square root over (LC)})−1                (L is an inductance value of an inductor, and C is a capacitance value of a capacitor).        
As can be seen from the above discussion, related art EM-type touch panels determine the contact point of a stylus pen using the resonance frequency of transmitted electromagnetic fields, thereby detecting contact points according to a completely different method resistive-type touch panels use to detect contact points. The EM-type touch panel has high endurance characteristics and high-quality image transmission. Because the stylus pen is arranged within the generated electromagnetic field, the location of the stylus pen relative to the EM-type touch panel can be detected even when it is above the passivation layer so that hovering and variable pressure effects can differentiated. Further, contact objects, lines may be drawn using contact objects other than a user's finger. EM-type touch panels, therefore, are commonly designed for use in settings such as conferences, seminars, etc., to eliminate the number of potential contact objects from disturbing the EM-type touch panel. The related art EM-type touch panel, however, has a complex circuit structure and is difficult to integrate with existing liquid crystal display modules (LCMs). Moreover, related art EM-type touch panels respond only to corresponding stylus pens, thereby making it difficult apply EM-type touch panels for use in certain applications (e.g., industrial fields). Lastly, if a contact object such as a user's finger contacts the related art EM-type touch panel, no contact points are detected. Accordingly, if a stylus pen becomes lost or damaged, the EM-type touch panel becomes inoperable until a new stylus pen is provided.